1. Field of the Invention
The present invention relates to the field of microelectronics. It relates in particular to an electronic circuit including a substrate having a plurality of conductor tracks applied to a top side of the substrate, a semiconductor chip arranged at a distance from the substrate on the top side thereof and electrically connected to the conductor tracks by means of solder connections at given points, and a solder stop layer provided on the conductor tracks between the conductor tracks and semiconductor chips and surrounding the solder connections, as well as a method of production thereof. Circuits of this kind are known from the prior art under the name of "flip-chip" mounting.
2. Discussion of Background
When soldering flip-chips (these are "naked" semiconductor chips with solder pellets (so-called bumps) as contacting elements) onto a substrate provided with conductor tracks, the use of a solder stop layer is advantageous and known.
This solder stop layer prevents the solder spreading out along the conductor tracks and consequently the semiconductor chip coming to rest on the substrate and causing undesired short-circuits.
Conventionally used for the solder stop layer is an organic solder resist which is usually applied in a screen printing technique or as a photolithographically processed fluid or film onto the substrate.
A solder resist of this kind has however the following disadvantages when used for flip-chip soldering:
poor temperature stability; and too high layer thicknesses which cannot be reproduced exactly. PA1 if the layer thickness is too small, the alignment effect of the edges is lost; PA1 if the thickness is too great, on the other hand, the soldering becomes irregular and leads to a defective contact between chip and substrate.
Since when fixing the flip-chips the edges of the solder stop layer serve at the same time to align the chip on the substrate, a layer thickness which cannot be reproduced has the following consequences: